Would it be possible to replace the trimmers with Bourns 3362, 3386 or similar encapsulated types? Bourns also have white and grey types apart from the usual blue models.
/Martin On Friday, 28 January 2022 at 05:10:27 UTC+1 Terry S wrote: > Is this printing on a PCB? Not clear from your photos. > > It seems unlikely that ink used on a PCB would be conductive. > > > On Thursday, January 27, 2022 at 2:52:25 PM UTC-6 Robert L wrote: > >> Hi folks, >> >> A friend received a rather nasty shock from one of his Mr. Nixie ITS-1A >> clocks... To add insult to injury, he dropped the clock when shocked and >> two tubes were broken. >> >> I've repaired his clock and, in the process, identified and mitigated the >> shock hazard. Note that I am not connected with Mr. Nixie. I'm simply >> trying to help others avoid this nasty experience. >> >> Here's what I found... >> >> 1) The black bottom case cover with labels for "SET", "ADJ" and "ALM" is >> likely printed using a carbon black based ink... Whatever the ink used, >> it's conductive. >> >> 2) There are 6 trim pots on the tube carrier assembly used to >> individually adjust -270V supplied to each of the six tubes. Tabs on the >> trim pots are directly over the conductive black printed base plate. >> >> The trim pot mounting tabs on my friends clock had come into contact with >> the conductive printed label. My friend touched the label and a grounded >> piece of the clock and was rewarded with the rather nasty shock. >> >> The photos below show the mitigation I used on my friends clocks. >> >> The mitigation is to assure that the trim pot tabs do not contact the >> black label plate. I added a triple thickness of Kapton tape between the >> trim pots and the label plate on his clocks. This may not be the best >> possible solution, but it's a starting place. I leave it to each of you to >> find a mitigation that you feel is safe. >> >> I urge you to check your ITS-1A clock for this hazard and mitigate as you >> see fit. >> >> I used a DVM to measure the voltage with one probe to the supply ground >> and the second probe touching the black printed label. I could also measure >> resistance between these two points with the clock unplugged. There should >> be an open circuit between these points - no voltage / open circuit >> between these points. >> >> A visual check will let you see if there's clearance between the trim >> pots and the label plate. I strongly recommend that you mitigate the hazard >> - clearance or not. At a minimum, I think that you want a non-conductive >> barrier between the trim pot tabs and the conductive label. >> >> Trim pot tabs are very close to the conductive label plate on the clock >> shown below... tabs were touching on the clock that shocked my friend:: >> >> [image: PXL_20220127_175801532.jpg] >> >> This is the clock that shocked my friend. The photo shows a triple >> thickness of Kapton tape separating all of the trim pot tabs from the label >> plate. Tape is held in place by adhesive backing and is also trapped >> between the tube carrier and label plate: >> >> [image: PXL_20220127_180629685.jpg] >> >> This hazard and a possible mitigation posted here in the hope that it >> prevents others from receiving a nasty surprise! >> >> All best regards, >> Bob >> >> >> -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/6e7b2822-f2a3-4aaa-942c-3e3535e9a9b4n%40googlegroups.com.
